With respect to its use as a dry break valve, semi-conductor manufacturing involves building up layers of conducting and insulating films on silicon wafers to produce miniature transistors. These films are deposited or etched using reactive gases, liquified gases or liquids. It is imperative to get precise properties of the films and to get repeatability from wafer to wafer. One of the requirements for achieving precision is to deliver exactly the flow rate of gas called for by the process and at exactly the required pressure and temperature. This is achieved by using several reactant delivery components. These are arranged into a "gas box" (sometimes called a "gas panel" or a "gas jungle" or a "gas tray"). A gas box contains an assembly of "gas sticks," each of which monitors and controls the flow of one gas to the process chamber. A gas stick is built around a component called a mass flow controller. The mass flow controller controls the flow rate of gas (or in some instances liquid). It is a thermal based device that reads the flow rate based on the temperature rise of the gas as it passes through the device. The temperature rise is calibrated to flow for the particular gas.
At the completion of the construction of the mass flow controller, the manufacturer may purge the mass flow controller with a gas such as dry argon. At the completion of the purged cycle, it is desired that the purge gas (i.e., dry argon for example) be maintained in the mass flow controller under a pressure on the order of 2 psig during shipment of the mass flow controller to the customer.